An interesting question. Many people would say that grammar doesn’t change. They would argue that there are fixed rules about grammar and that native speakers follow these rules (consciously or unconsciously) and that there is general agreement about what constitutes an error. Changes in grammar happen more slowly and gradually than changes in other areas of language. For example, vocabulary is more flexible and usage can change. All this points to a fixed grammatical system.

However, there are differences in grammar over time and between speakers of different nationalities. This can be illustrated by comparing texts from the time of Shakespeare and today; you can see that grammatical structure is not the same. There are also differences across nationalities; for example the way the present perfect is used in the USA and the UK.

All in all, it is difficult to say whether grammar changes without knowing more about the context of the question.